76 Intelligence and Miscellaneous Articles. 



QUANTITATIVE PHOTOGRAPHIC INVESTIGATION OF ELECTRICAL 

 OSCILLATIONS. BY J. MIESLER. 



The object of the present research is to show the agreement 

 between the times of oscillation of the Leyden Jar as found pho- 

 tographically, with the times calculated from the measured capa- 

 cities and the coefficient of self-induction of the jars and the 

 circuit ; there being as yet no long comparative series of numbers. 

 The photographs were taken by meaus of a rotating plane mirror 

 and an object-glass. The times of rotation were then deduced from 

 the dimensions of the photographs. 



The coefficient of self-induction of the wire used in each case 

 was determined by a null method by comparison with a condenser 

 divided into thousandths of a microfarad. The capacities of the 

 Leyden jars used in the separate observations were compared with 

 this condenser by meaus of an electrometer. The time of vibra- 

 tion was determined from these two last series of data by means 

 of the formula 



T = ttVCL, 



and compared with those deduced from the photographs, and it 

 was found that there was a very close agreement. The thickness 

 of the wires was always 0-8 mm., so that the above formula holds 

 strictly for thin wires. — Wiener Berichte, July 1890; Beibl'dtter 

 der Physik, No. 11, 1890. 



ON THE SMALLEST PERCEPTIBLE VISUAL ANGLE IN THE VARIOUS 

 PARTS OF THE SPECTRUM. BY W. UHTHOFF. 



A spectrum more than 20 cm. in length was projected from 

 zirconium light, through a large prism filled with cinnamic ether, 

 and corresponding lenses, from which in seven places a portion 

 3 mm. in diameter could be cut off by a sliding metal screen. If 

 the eye looked through the aperture of this screen, it saw the 

 nearest face of the prism illuminated by the corresponding homo- 

 geneous colour. A wire grating could be moved backwards and 

 forwards in the path of the rays. The wires were at a distance in 

 the mean of 0*0926 mm. apart, and the intervals were exactly 

 equal to the thickness of the wire. Prom the distance from the 

 eye at which the grating had to be placed, so that the wires were 

 just invisible, the sharpness of vision could be deduced for the 

 various colours. This was almost the same for all colours ; in the 

 case of the author the smallest visual angle under which the eye 

 could distinguish the object (the breadth of a wire and the space 

 taken together) was 55*2, and for A. Kbnig 65*6 seconds, from 

 which it is inferred that the diameter of the elements in the retina 

 concerned in this is 0-002 to 0*004 mm. — Zeitschrift fur Psychol, 

 und Physiologic, i. p. 155; Beiblatter der Physik, No. 11, 1890. 



